A scanning device is known in which a two-part tape-guiding drum is provided and in which a rotary headwheel disk is in the gap between the two parts of the drum. At the periphery of the headwheel disk two magnetic heads are affixed. The signal transmission from and to these magnetic heads takes place over planar rotary transformers. One of the planar rotary transformers is located at the upper side of the rotary drum and the other is located at the underside of the rotary drum. Such a scanning device, however, is suitable only for recording and playback of relatively narrowband signals.
For recording and reproduction of broadband digital signals at a data transmission rate greater than 1 gigabit per second, the data stream is subdivided for transmission simultaneously over several channels. In order to limit the circuit expense resulting from the subdivision it is desirable that the individual rotary transformers all have the same signal transmission properties. In such a case the frequency bandwidth should accomodate a data rate above 100 megabits per second and the signal to noise margin between the individual rotary transformers should be greater than 80 dB.
Known devices with a number of planar rotary transformers (DE 33 42 493 C2) do not satisfy these requirements, because the individual transformer windings are concentrically disposed at different radii and the signal to noise margin is insufficient.
Another known kind of embodiment (DE 26 09 335 A1 and U.S. Pat. No. 4,156,261), in which the individual rotary transformers are constructed with two magnetic core rings which are disposed one above the other, has the disadvantage that the signal to noise margin, especially for rotary transformers used respectively for recording and playback, is insufficient to meet the above-mentioned requirements. There is also the further disadvantage that replacement of the headwheel disk after wearing away of the magnetic heads is expensive.